We intend to study: 1) the various factors involved in the interaction between glycosaminoglycans (GAG) and lipoproteins isolated from plasma; 2) the rheological consequences of such interaction; 3) the level of plasma GAG in subjects with evidence of ischemic heart disease. Plasma GAG may be separated into two species on the basis of sulfate content. The less abundant, highly sulfated species reacts with HDL and LDL and increases their viscosity; the other, more abundant and less sulfated species binds lipoproteins without producing rheological modifications; rather, it protects them from the unfavorable effects of interaction with the less abundant species. To perform these studies with amounts of GAG and lipoproteins approaching their physiological levels and proportions, use is made of pyrene-labeled lipoproteins. These show a specific, two wavelength fluorescence emission whose modifications indicate changes in the conformation of the labeled molecule. Lipoproteins deposition in the arterial wall is considered relevant to the development of initial atherosclerotic plaques. Hypertension and hyperlipoproteinemias favor such deposition but nothing is known concerning the mechanisms which make the lipoproteins less soluble or more prone to adhere to the vascular walls. Our pilot studies suggest that 1) two normal components of plasma, upon interaction, may create a situation favorable to lipoproteins deposition; 2) deviation from the physiological balance between two types of plasma GAG may cause unfavorable rheological conditions in the presence of normal levels of lipoproteins. A detailed knowledge of the factors which favor the interaction between plasma GAG and lipoproteins may open the way to practical interventions tending to minimize, reverse or prevent them and their unfavorable consequences.